This invention relates to a sewing machine, particularly to an improvement of a presser foot control device for narrowing the space of the device occupied and decreasing the power when an electromagnet works.
The presser foot of a sewing machine is designed to keep cloth flat and wrinkleless and moves the cloth smoothly by means of a feed dog. Lifting and lowering of the presser foot is effected by up-and-down movement of a working rod of an electromagnet placed vertically under a plate base.
The detailed structure of the electromagnet and working rod is shown in FIG. 6. The electromagnet 20 is is positioned vertically under the plate base 10, secured on a position plate 30 fixed with plural position posts 101 extending down from the plate base 10. The position plate 30 has a vertical ear 301 at an end and pivotally connected to a middle section of a lever rod 302, which has a slot 303 at one end for a pin 304 to insert through and connected with a working rod 201 of the electromagnet 20. Further, the lever rod 302 has the other end connected to a lower end of a connecting means 40 such as a chain. The connecting means 40 passes through the plate base 10 and has an upper end connected to a swinging arm 50 that is connected to a moving device of the main mechanism 60. The moving device moves the presser foot 70. When the presser foot 70 is above the surface of the slide plate 80, a pedal is able to be stepped on to electrify the electromagnet 20 to pull up the working rod 201, with the left end of the lever rod 302 pulled up to cause the right end of the lever rod 302 move down and pull down the connecting band 40. Then the swing arm 50 swings down, with the presser foot 70 lifted up by the moving device. On the contrary, when the pedal is no longer stepped on, the electromagnet 20 is not electrified, freeing the working rod 201 to slide down, with the presser foot 70 moving down by means of the lever rod 302, the connecting band 40 and the swing arm 50 being interconnected to one another.
However, when the working rod 201 is pulled inward (i. e. moving up), the weight of the magnet in the electromagnet 20 plus the gravitational force, and friction associated with lever rod 302, the connecting band 40, the swing arm 50, etc., i.e. the force of lifting the working rod 201 is substantially high so that the power required by the electromagnet 20 will be large. In addition, the electromagnet 20 may be hit by a leg of a user, as the electromagnet 20 is positioned vertically the plate base 10, or the user may worsen his/her bodily posture by trying to avoid the electromagnet 20. Besides, the working rod 201 of the electromagnet 20 is connected to the slot 303 of the lever rod 302 by means of the pin 304, so when the working rod 201 is retracted the pin 304 is liable to slide in the slot 303, wasting the power of the electromagnet 20. The sliding back-and-forth movement of the pin 304 in the slot 303 forms a kind of friction to waste the power of the electromagnet as well.